1. Field of the Invention
This invention relates to drawing output units for recording drawings through processing of code data for preparing the drawings.
2. Description of the Prior Art
CAD (Computer Aided Design) systems for designing drawings by means of computer have widely been utilized for machinery and equipment as well as development for various electronic devices and the like.
CAD systems have been variously employed over a range of from so-called stand-alone type systems to large scale systems wherein a number of intelligent terminals 2 are connected to a host computer 1 as shown, for example, in FIG. 1. Such design drawings which were prepared in the latter large scale systems are stored in memories or the like of the host computer with a given data format. For instance, when drawings are outputted in the respective terminals 2 of FIG. 1, a given communications protocol is executed between the terminals 2 and the host computer 1 through a communication control equipment 3 to fetch in the terminals the drawing data stored in the memories.
FIG. 2 is a perspective view illustrating the case where such drawings are outputted by the use of a pen plotter 5 in which a prescribed command is inputted through a keyboard 2a of a terminal 2 by an operator to call the host computer thereby requesting transfer of said drawing data, so that the drawing data are successively transferred from the host computer 1.
The aforesaid drawing data are those obtained by collecting element information for forming one pattern (e.g., image or circle) by the number of patterns to be recorded in the drawings. For example, if certain element information is that relating to a straight line, such element information is composed of a code datum (vector information) for instructing to draw the straight line and two code data showing coordinates of starting and end points of the straight line, i.e., three code data in total. Furthermore, if element information is that as to 1 circle, such element information consists of a code datum for instructing drawing of the circle, a code datum for instructing to paint out the circle black, and code data for indicating a coordinate of the center as well as the radius, i.e., four code data in total. Moreover, there are various code data such as that for instructing polygon and the like.
When one of such element information is inputted, the pen plotter 5 draws a prescribed pattern on a recording paper 7 as a result of operation of amount and direction in the movement of a pen 6 from the coordinate positions of starting and end points in the case, for example, where straight line is drawn. In this case, when processing of one element information is completed, the following element information is processed, and when the final processing of element information is completed, output of the drawings is simultaneously finished.
In such operation, the pen plotter 5 repeats a series of operations as illustrated in FIG. 3. More specifically, the element information is first read (step S1), the command is decoded (step S2), the predetermined operation is effected (step S3), the starting point is set and the pen is put down on the prescribed position (step S4), the motor is driven to detect position of the pen and said pen is transferred to the end point while being in a feedback state (steps S5 and S6), and when the pen reaches the end point, the motor is stopped to put up the pen, thereafter the pen is returned to the starting position (step S7).
As described above, the drawing output unit wherein such pen plotter is utilized requires no conversion of element information into raster information, because when the element information is processed one by one in order, output of the drawing is completed without any additional processing, so that such data processing system can be simplified. On the other hand, there is such a disadvantage in that the manner for preparing drawings in this case is that in accordance with similar mechanical operation to handwriting one, so that a long period of time is required for outputting complicated drawings.
On one hand, an electrostatic plotter has been well known as a drawing output unit in place of the aforesaid plotter.
In the electrostatic plotter an electrostatic latent image is formed on a special recording paper by the use of an electrostatic multi-stylus head provided with needle-like discharge electrodes, and the resulting latent image is developed with use of liquid or powder toner. In case of using such an electrostatic plotter, a fixed amount of element information has previously been converted into such raster information composed of picture signals corresponding to an actually recorded image to store the raster information in memory.
The electrostatic multi-stylus head has such construction that a number of aligned needle-like electrodes 11 are longitudinally divided into a predetermined number of blocks as shown in, for example, FIG. 4 wherein picture signal is supplied to the respective electrodes through signal lines 12. Discharge voltage is fed to the respective blocks through power source lines 13. When the discharge voltage is applied at a time, load of the power source becomes excessive so that the discharge voltage is successively supplied to the respective blocks in accordance with time sharing manner.
In view of a construction of such recording head as described above, the electrostatic plotter divides drawings to be outputted into a plurality of areas corresponding to the blocks of the recording head, the element information in every area is converted into raster information, and the resulting information is supplied to the head through the signal line 12. On one hand, discharge voltage is supplied to the corresponding blocks through the power source line 13 thereby effecting recording in that region, and similar operations are repeated in respect of the other blocks. Such system involving the above described steps has generally been adopted, but this system has had a disadvantage in that both of processing of signal and outputting of drawing cannot be sufficiently speeded up.
Furthermore there are laser printers utilizing electrophotographic method as a unit which can record such raster information at high speed. These laser printers use a system wherein raster information is converted into a light beam in every page, the converted light beam is introduced to the outer surface around a photoreceptor to form an electrostatic latent image, and the resulting photoreceptor is developed with the use of toner.
In order to employ such type of printer, however, it is required that all the element information in each page has previously been converted into raster information.
Besides, once recording operation was started in such a printer just described above, a series of operations proceed until the completion of recording for one page, so that any pause and interruption cannot be permitted in the course of such step. For this reason, it is required that acceptance of element information from an external system and processing for conversion of the element information into raster information can efficiently be carried out so that continuity of such recording operations is not interrupted.
In order to realize such acceptance and processing for conversion, there may be considered such system wherein a memory for storing element information and a memory for storing raster information, or a printer controller and the like are connected to a general bus line as is used in conventional computers, and those connected to the general bus line are subjected to time sharing control by means of a central processing unit. However, in the case of recording operation where raster information is transferred to a printer at high speed, all the other processing must be stopped so that there is a problem in view of efficiency in the system.
Besides, a long period of time is required for converting such element information consisting of complicated drawing into raster information, and in this connection it is difficult to realize faster conversion.
Furthermore such element information which concerns drawings to be outputted to the printer and is transferred either in response to the request from terminals, or automatically from the host computer or other systems comprises both the information which should be quickly outputted and the other information without any urgency. In this respect, indiscriminate processing for such information in accordance with the order of input is not favorable from viewpoint of efficiency in the system. Moreover there is a case where it is frequently requested to enlarge or reduce (scale up or down) drawings. In this case, it is necessary either for providing a dedicated processor or the like therefor, or that the information is subjected to required processing, and then such information is transferred to the drawing output unit. However, such arrangements as described above bring on difficulty such that load of installation cost or the host computer becomes larger.
The present invention has been made for eliminating the above-mentioned disadvantages and problems.